1. Field of the Invention
The production of seals and coatings and the bonding of tiles or floor coverings
The invention relates to methods of producing seals and coatings and of bonding tiles or floor coverings by applying compositions based on aqueous acrylate copolymer dispersions which have a filler content of at least 20% by weight and which are free from major amounts of volatile organic solvents, plasticizers and modified or unmodified natural resins of low molecular mass. The invention also relates to the use of such compositions as sealants, coating materials or single-side adhesives (adhesives for one-sided application).
2. Description of the Background
The development of new kinds of polymer dispersions based on acrylate more than 25 years ago saw a significant turning point in the processing of sealants and in the work involved in laying tiles and floor coverings. It was possible to provide the processor with sealants, coating materials or single-side adhesives in whose processing the risks were very greatly reduced relative to the processing of the rubber solutions which had been dominant up to that time, since only 5% rather than 75% of flammable solvents were released. Sealants, and single-side adhesives used for tiles or floor coverings, differ fundamentally from pressure-sensitive adhesives in their use and in the properties which are required for that use. Pressure-sensitive adhesives are, in general, systems having an overall high surface tack and are unfilled systems, i.e. contain no fillers. In contrast to sealants and single-side adhesives they are applied as thin films (film thicknesses of about 20 to 200 xcexcm) and for this reason alone require very different polymer mechanics. The requirements for single-side adhesives are application of the composition to one side only, and also the ability to correct the laid tiles or floor coverings in the course of processing, the ability to remove fresh residues of composition from the tiles or floor coverings and from the tools using water, and also excellent aging resistance. These special requirements have also led to special test standards, such as the testing of peel and shear strength and the testing of the wet bonding capacity and the dry gripping capacity.
The aqueous, acrylate copolymer-based dispersions which it has been possible to obtain commercially to date as sealants or for the fixed laying of tiles or floor coverings include not only at least 20 percent by weight of filler but also relatively large amounts of organic solvents and/or plasticizers, a part of which escapes into the atmosphere as the system sets, or they include a relatively large proportion of low molecular mass resins, such as balsam resins or colophony resins. The presence of these resins, however, is a problem since they mayxe2x80x94as compounds of low molecular massxe2x80x94migrate, can be washed out, cause color changes, owing for example to oxidation or to impurities in the mixture, reduce the polymer strength, or else may be toxicologically objectionable.
It is an object of the present invention to discover improved compositions, based on aqueous acrylate copolymer dispersions containing at least 20% by weight of filler, for the production of seals, coatings, including impregnated systems, and for the bonding of tiles or floor coverings, which compositions comprise as far as possible no volatile organic solvents, plasticizers or low molecular mass resins, such as natural resins or modified natural resins, and which do not have the abovementioned disadvantages of the aqueous acrylate copolymer dispersions currently used for the methods, or which have such disadvantages only to a markedly reduced extent.
We have found that this object can be achieved, by applying compositions based on aqueous acrylate copolymer dispersions, containing at least 20% by weight of fillers, as sealants, coating materials (including impregnating materials) or single-side adhesives, if use is made of a filler-containing aqueous dispersion of a polymer mixture comprising a) a polymer A having a K value of from 5 to 55 and a glass transition temperature of below xe2x88x9210xc2x0 C., containing at least 50% by weight of copolymerized acrylic ester units, and b) a polymer B which is an acrylate copolymer having a glass transition temperature of from xe2x88x9250 to +50xc2x0 C.
The invention accordingly provides a method of producing seals and coatings, including impregnated systems, and of bonding tiles or floor coverings by applying an acrylate copolymer dispersion which has a filler content of at least 20% by weight and which is free from major amounts of organic solvents, plasticizers and modified or unmodified natural resins of low molecular mass, which comprises applying an aqueous dispersion, containing at least 20% by weight of filler, of a polymer mixture comprising
a) a polymer A having a K value of from 5 to 55 and a glass transition temperature of below xe2x88x9210xc2x0 C., at least 50% by weight of which comprises copolymerized units of at least one ester of acrylic acid, and
b) a polymer B which is an acrylate copolymer having a glass transition temperature of from xe2x88x9250 to +50xc2x0 C.
The use of filler-containing aqueous acrylate copolymers as solvent-free single-side adhesives for floor coverings is known from EP-A 490 191. The compositions described therein, although free from solvent, necessarily include, however, a plasticizer and a resin. (Filler-containing aqueous acrylate copolymers for checked floor coverings, which are essentially free from organic solvents, plasticizers and resins, are described in EP-A 743 965. The dispersions described therein of acrylate polymers having glass transition temperatures of less than xe2x88x9225xc2x0 C. correspond to the preferred polymers B in accordance with the present invention. EP-A 743965 does not describe a novel mixture of the polymers B with the polymers A.) In comparison to the dispersions of polymers B described in EP-A 743 965, the dispersions of the novel mixtures of the polymers B with the polymers A have improved processing properties when used as single-side adhesives for floor coverings, in terms of better fixing in the wet and dry state and of freedom from odor. Furthermore, they have surprising advantages in respect of adhesion to rubber and of a particularly high heat stability.
The dispersions used in accordance with the invention contain preferably less than 3% by weight, in particular less than 1% by weight, of the abovementioned solvents, plasticizers and natural resins. With particular preference they are completely free from these components.
The polymers A used in accordance with the invention for the mixture with the polymers B have a K value of from 5 to 55, (preferably from 5 to 30,) and a (glass transition temperature of below xe2x88x9210) and preferably from xe2x88x9220 to xe2x88x9260xc2x0 C. and contain at least 50% by weight of copolymerized units of at least one ester of acrylic acid. (The polymers A have a polydispersity Mw/Mn of from 1 to 10, and preferably from 1 to 5, which is a measure of the breadth of the molecular weight distribution of the respective polymer.)
(The K values of the polymers used in accordance with the invention are determined in accordance with DIN 53726 in a 1% strength by weight solution in tetrahydrofuran at 25xc2x0 C.) The glass transition temperature Tg is determined with the aid of the DSC (Differential Scanning Calorimetry) method in accordance with ASTM 3418/82. For copolymers it can be calculated in approximation from the glass transition temperatures of the homopolymers of the corresponding monomers by the equation of Fox (T. G. Fox, Bull. Am. Phys. Soc. (Ser.II) 1 (1956) 123)             1      Tg        =                            X          1                          Tg          1                    +                        X          2                          Tg          2                    +      ⋯      +                        X          s                          Tg          s                      ,
where X1, X2, . . . Xs are the mass fractions of the monomers 1 to s and Tg1, Tg2, . . . Tgs are the glass transition temperatures of the homopolymers of the respective monomers 1 to s in kelvins. The glass transition temperatures of the homopolymers of common monomers are known and can be found in the technical literature, for example in J. Brandrup, E. H. Immergut, Polymer Handbook, 2nd Ed., J. Wiley, New York 1975.
The (polydispersity Mw/Mn) is determined by the customary methods of gel permeation chromatography, carrying out molar mass calibration with polystyrene.
The polymer A is in most cases a liquid polymer which may also be in the form of a fine aqueous secondary dispersion. Highly suitable polymers A contain, in copolymerized form,
a) from 70 to 99% by weight of acrylates which form homopolymers having glass transition temperatures of from xe2x88x9230 to xe2x88x9260xc2x0 C. and preferably from xe2x88x9240 to xe2x88x9260xc2x0 C.,
b) from 1 to 30% by weight of carboxyl- and possibly hydroxyl-containing, olefinically unsaturated, copolymerizable monomers, and
c) from 0 to 29% by weight of other olefinically unsaturated, copolymerizable monomers.
Also very advantageous are polymers A which comprise, in copolymerized form,
a) from 85 to 98% by weight of alkyl acrylates, which form homopolymers having a glass transition temperature of from xe2x88x9240 to xe2x88x9260xc2x0 C., and
b) from 2 to 15% by weight of carboxyl- and possibly hydroxyl-containing monomers.
Examples of suitable monomers a) are n-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, decyl acrylate and dodecyl acrylate. Examples of suitable monomers b) are monoolefinically unsaturated, copolymerizable carboxylic acids having 3 to 5 C atoms, their anhydrides and monoesters, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, maleic anhydride and mono-butyl maleate. Examples of suitable monomers b) containing hydroxyls are 2-hydroxyethyl acrylate and methacrylate, hydroxypropyl acrylate and methacrylate and 4-hydroxybutyl acrylate and methacrylate. Suitable monomers c) are vinyl esters of monocarboxylic acids having 2 to 18 C atoms, such as vinyl acetate or vinyl propionate, acrylates and methacrylates not included in a), such as methyl methacrylate or ethyl acrylate, vinyl- and alkenylaromatic monomers having 8 to 18 C atoms, such as styrene, xcex1-methylstyrene or vinyltoluene, amides of olefinically unsaturated carboxylic acids having 3 to 5 C atoms, such as acrylamide or methacrylamide, N-vinyl monomers, such as N-vinylpyrrolidone or N-vinylcaprolactam and amino-containing olefinically unsaturated monomers, such as dimethylaminoethyl acrylate or dimethylaminobutyl acrylate. Acrylate copolymers A which comprise carboxyl-containing monomers such as acrylic or methacrylic acid in amounts from 1 to 10 and, preferably, from 1 to 5% by weight in copolymerized form are particularly advantageous. The nature and amounts of the monomers in mixtures should be chosen so as to give polymers A which meet the provisos in respect of monomer amounts and glass transition temperatures of the polymers. It has proven judicious to prepare the polymer A with properties such that it markedly increases the tack of the mixture M after the drying thereof.
The polymers A can be (prepared in a manner known per se:) for the preparation of polymers A having a very narrow molecular weight distribution (Mw/Mn close to 1) a known process of high-temperature polymerization should be employed. (The polymers A are preferably prepared by polymerization in bulk or in solution at from 60 to 220xc2x0 C. possibly using, for solution polymerization, customary organic solvents) such as hydrocarbons (e.g. toluene), alcohols (e.g. isobutanol), esters (e. g. ethyl acetate) or ketones (e. g. methyl ethyl ketone) with appropriate boiling ranges or establishing the relatively high polymerization temperature in closed reactors under pressure (up to 15 bar) in the case of volatile solvents. The customary polymerization initiators can be employed, in known amounts. In view of the (desired low K values and molecular weights of the polymers A) it is sensible to use polymerization regulators, such as mercaptans, examples of which include mercaptoethanol, mercaptosuccinic acid, 3-mercaptopropyltrimethoxysilane and, in particular, dodecyl mercaptan. (In view of the nature of the use of the polymers A in accordance with the invention it is sensible to carry out extensive removal of volatile impurities such as residual monomers from the polymers A prior to use.)
(Once prepared, the polymers A can be processed further to give the mixtures that are used in accordance with the invention, with the polymers B, advantageously by incorporating the liquid polymer A directly by emulsification into a dispersion of the polymer B, with monitoring and adjustment of the pH.) Especially in the case of carboxyl-containing polymers A it is often also advantageous to process the polymer A under alkaline conditions by the customary methods of polymer emulsification to give a secondary dispersion which can then, for example, readily be stirred together with the aqueous dispersion of the polymer B. The proportions of the polymers A and B in the resulting mixture M can be very different, although it is usually judicious for the polymer A to be present in a smaller amount than the polymer B in the mixture of A+B. The mixture of A+B advantageously contains from 1 to 49 parts of polymer A and from 51 to 99 parts of polymer B, preferably from 25 to 45% by weight of the polymer A and from 55 to 75% by weight of the polymer B, based in each case on the 100% polymers.
The (polymers B) are (meth)acrylate copolymers having a glass transition temperature of from xe2x88x9250 to +50xc2x0 C., in particular of below xe2x88x9225xc2x0 C. and, preferably, of below xe2x88x9230xc2x0 C. They (preferably have molecular weights Mn of more than 20,000.) Highly suitable polymers B contain at least 50 and, in particular, from 60 to 100% by weight of at least one ester of acrylic acid and/or of methacrylic acid, in copolymerized form. Examples of suitable esters are C1-C12-alkyl acrylates, such as methyl, ethyl, n-propyl, n-butyl, 2-ethylhexyl, decyl and dodecyl acrylate and also n-butyl methacrylate and n-hexyl methacrylate.
Preference is given to those monomers which form homopolymers having glass transition temperatures of from xe2x88x9240xc2x0 C. to xe2x88x9260xc2x0 C.
Preferred polymers B contain from 0.5 to 10 and, in particular, from 0.5 to 5% by weight of a copolymerizable, olefinically unsaturated carboxylic acid having 3 to 5 C atoms or the anhydrides or monoesters thereof in copolymerized form, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid and maleic anhydride or mono-n-butyl maleate.
Further comonomers which are particularly suitable for the polymers B are the comonomers specified above for the polymers A for b) and c).
Examples of highly suitable copolymers B are those which in addition to xe2x89xa750% by weight of alkyl(meth)acrylates, methyl methacrylate, vinyl acetate, vinyl propionate and/or styrene, in an amount of up to 30% by weight, also contain carboxyl- and possibly hydroxyl-containing monomers in an amount of in each case not more than 5% by weight, the copolymers B having glass transition temperatures of below 25xc2x0 C. (The polymers B can be prepared advantageously by solution polymerization and subsequently converted conventionally into polymer dispersions;) (preferably, however, they are prepared by emulsion polymerization, so that aqueous polymer dispersions can be obtained directly. The preparation of the polymers B is described in EP-A 743 965, the relevant content of which is incorporated herein by reference.) The solids content of the resulting polymer dispersions is, in particular, from 40 to 75% by weight.
For the use of mixture M comprising the polymers A and B, which can take place as indicated above, the mixture is admixed with the (mineral fillers, such as finely ground or precipitated chalks having a mean particle diameter of in general from 2 to 50 xcexcm or quartz flour) having a mean particle diameter of from 3 to 50 xcexcm, and also wetting agents or dispersants, thickeners, and, if desired, further additives, such as antifoams and preservatives. The water content of the ready-to-use compositions is in general from 7 to 50% by weight, in particular from 10 to 30% by weight, based on the overall aqueous formulation.
The filler-containing aqueous formulations with the mixture M comprising the polymers A and B is suitable as a single-side adhesive for floor coverings of, for example, polyvinyl chloride in configurations as multilayer coverings or homogeneous coverings, foam coverings with a textile backing, for example jute, polyester nonwoven, rubber coverings, textile coverings with various backings such as polyurethane foam, styrene-butadiene copolymer foam, a textile secondary backing, needlefelt floor coverings, polyolefin coverings or linoleum coverings, on substrates such as wood, screeding, concrete, ceramic tiles, metal substrates or other suitable substrates.
The aqueous formulation with the polymer mixture used in accordance with the invention can be applied to a substrate using, for example, a toothed applicator. After customary venting, the floor covering is then laid. In terms of processing the novel compositions resemble the solvent-containing single-side adhesives. The compositions used in accordance with the invention feature a good level of performance properties such as peel strength, shear strength, wet bonding capacity and dry gripping capacity and a high heat stability.
The following examples and comparison experiments illustrate in more detail the methods of the invention without limiting them. Unless otherwise indicated, parts and percentages are by weight. The K values, glass transition temperatures and Mw/Mn ratios were determined and/or calculated as indicated in the text above.